Where the hell did that come from?

[Bushbasher]

Ok, I have a little story to tell then we'll get to the question, I'll try to be brief:-

Pulled a trailer to Adelaide a couple of weeks ago and an hour into the trip the car, (AUII wagon in sig. below), suddenly starts randomly downshifting ; sometimes on the slightest of rises in the road, sometimes for no reaon at all except maybe a gust of wind, who knows. Anyway, I thought trans was playing up till I rested my foot on the throttle and while on cruise I could feel it flooring itself slowly till it downshifted even though there was no corresponding acceleration, like it was starving for fuel, but hang on, we're running on LPG. I stop, pop bonnet and check all the lines and converter and solenoid connections etc. but everything looks ok so I put up with it till we got to Adelaide then had a proper look. Couldn't find anything except the coolant was suddenly way down; bugger, must have sprung a leak somewhere says I. Topped up and put up with issue all the way home thinking it must be the converter.
Got home and stripped the converter but it was perfect inside, not even a hint of residue of any kind and the coolant level hadn't moved again either. I'm stumped, hmmmm.
Fast forward a week and the missus is off to work yesterday morning but only gets 2kms before the car dies and won't start. I go and give her my car and get under the bonnet of the wagon and the coolant bottle is empty and the converter is frozen, shirt, says I, there's got to be an intermittent leak somewhere cos this is twice now in 2 weeks. I get the car home on petrol and top it up then use it to run to town and back to see what will happen. Now the temp gauge won't come up properly and hovers around the edge of the cold/normal line. Now I'm thinking either the temp sensor has had a heart attack due to the coolant loss or the thermostat is stuck open. So now I have 2 problems, or is it 3? Coolant loss, fuel flow issue and now a temp problem.
Now we get to the question; I pulled the thermostat after crawling all over and under the engine looking for evidence of a coolant leak and finding nothing, and found this rubber washer jambed in the thermostat holding it open-






- it's about the size of a 20c piece. The break is where the thermostat bit it, but where the hell did it come from!

The engine was changed over about 150k ago as it was cheaper than doing a head swap at the time and the thing hasn't been touched since so if it's not part of the cooling system then it somehow made it's way into the block before or at the time of the change over and has been floating around in there for over 3 years.

I've put the car back together and everything seems to be back to normal but I'll just have to see if there is ongoing coolant loss but my theory is that pulling the trailer must have opened the thermostat enough and made enough flow to pick up the washer and deposit it in the thermostat housing partially blocking the heater pipe inlet thus causing the converter to be on the verge of freezing but not quite and every time the car downshifted and revved it forced enough coolant through the line to keep the converter alive. It also explains the temp gauge but what I can't figure out is how it forced out the coolant as the car never overheated at any time and a 50km drive yesterday showed no coolant loss and no puddles under the car. The missus has taken the wagon to work today with some extra water just in case but if there is no loss in the next week or so I'll go buy some more coolant and flush and refill the system.

So... does anyone recognise that washer and where it might have come from and does anyone have a theory on how it might have caused the coolant loss without overheating the engine noticeably cos I'm at a loss right now. If it caused a blockage that created enough back pressure to force fluid out the overflow then it should be cured but if it's forced the fluid past a gasket or seal somewhere else I'll need to do something about it although I'm buggered if I can find any evidence of fluid loss anywhere.

Cheers
Bushbasher